Locking device for the jaws of a mechanical grab



p 1965 P. F. MOSKOPF ETAL 3,207,548

LOCKING DEVICE FOR THE JAWS OF A MECHANICAL GRAB Filed Aug. 3, 1962 4 Sheets-Sheet 1 p 21, 1965 P. F. MOSKOPF ETAL 3,207,548

LOCKING DEVICE FOR THE JAWS OF A MECHANICAL GRAB Filed Aug. 3, 1962 4 Sheets-Sheet 2 F/G.3. I 38 40 3,207,548 LOCKING DEVICE FOR THE JAWS OF A MECHANICAL GRAB Filed Aug. 3, 1962 Sept. 21, 1965 P. F. MOSKOPF ETAL 4'Sheets-Sheet 3 MGR Vv Q

p 21, 1965 P. F. MOSKOPF ETAL 3,207,548

LOCKING DEVICE FOR THE JAWS OF A MECHANICAL GRAB Filed Aug. 3, 1962 4 Sheets-Sheet 4 United States Patent 3,207,548 LOCKING DEVICE FOR THE JAWS UP A MECHANICAL GRAB Peter Franziskus Moskopf, Heinrich Boden, and Heinrich Valentin Mengden, all of 21 Hermannstrasse, Neuwied, Rhine, Germany Filed Aug. 3, 1962, Ser. No. 214,671 Claims priority, application Austria, Nov. 6, 1961,

A 8,349/61; May 2, 1962, A 3,563/62 21 Claims. (Cl. 294104) This invention relates to mechanical grabs of the suspended bucket type such as are used for the picking up, transporting, and discharge of solid materials. It is particularly, although not exclusively, concerned with grabs designed for large flat articles whose upper surface is approximately horizontal; with such grabs it is desirable, in order to save labor, to provide means which will automatically lock the grab after the articles have been gripped and release them when they have been set down.

The invention presents a solution for this problem by linking to a jaw of the grab a feeler in the form of, for example, a cranked lever adapted to be moved by the load and whose one end actuates a pivotally mounted detent which, when the load is released, engages a projection or trip member on the other jaw of the grab so as to maintain the jaws in the open position.

It is an object of the present invention to provide that, when the load to be picked up is engaged by the feeler, the latter is displaced to automatically disengage the trip member and release the grab jaws so that they can grip the load; and although only the above-mentioned characteristics are necessary in the grab, the invention is advantageously applicable to that form of grab in which each jaw is constituted by a generally bell-crank shaped frame having at least two parallel side arms and at least two parallel bars joining the arms, the one extremity of one frame being pivotally connected to the angle of the other.

It is another object of the present invention that the said detent is actuated by a pawl formed at its free end as a hook engageable with the said feeler.

A further object of the invention is to provide that the said detent is free to pivot on the same jaw as that to which the said feeler is connected, and the said detent may be biased towards its operative position by a tension spring connected to the said pawl.

The free end of the pawl may be connected by another tension spring to the other jaw of the grab which carries the said trip plate or detent-engaging projection.

It may in certain cases be desirable to shape the pawlengaging end of the feeler as a fork which embraces the pawl.

Where the load to be picked up is sensitive to shock or impacte.g. slabs of green concrete-it may be damaged by the impact of the feeler if the co-operation of the several parts of the locking device is such that the grab jaws can close quickly upon making contact with the load. Furthermore,-the impact of the feeler itself on rapid lowering of the grab could subject the load to considerable shock and might cause undesirable damage.

Accordingly, it is envisaged by the present invention that the said pawl is elastically linked to the said detent, as by a tension spring so as to permit the feeler to yield on first impact with the load. The detent may itself be spring-loaded to the position of engagement with the said trip member.

According to a further aspect of the invention, the end of the pawl which is engaged by the said feeler may be arranged to rest on a fixed abutment when the grab arms are locked, said abutment disengaging the pawl from the said feeler when the grab jaws fall free.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings wherein:

FIGURE 1 is a perspective View of a conventional form of grab consisting of two pairs of arms and parallel load-gripping bars;

FIGURE 2 is a plan view of the grab of FIGURE 1 but showing a locking device according to the invention;

FIGURES 3 to 5 are similar side elevations showing the locking device according to the invention in three different positions;

FIGURE 6 is a plan view of a modified locking device according to the invention;

FIGURE 7 is a fragmentary section on the line VII VII of FIGURE 6 showing the positions of the parts when the grab is in the open position, and

FIGURE 8 is a section similar to FIGURE 7 showing the positions of the parts when the grab has already picked up the load.

In the drawings, like parts performing like functions are identified by similar reference numerals.

The conventional grab illustrated in FIGURE 1 consists of two pairs of cranked frames 1 and 2 constituting the jaws and which can be suspended in any desired manner, as from a traveling crane, truck derrick, or simply on a cable 4 anchored to a rod 3. The arrow 5 shows the lifting and lowering motion of the suspension which controls the entire grab. The two side arms 9, 11 and 10, 12, respectively of each jaw 1, 2 are connected by respective bars 6 which, in the position shown in FIGURE 1, have just gripped the load 8. Any downward movement of the suspending tackle 4 causes the jaw bars 6 to move in the direction of the arrows 7 and release the load 8. Thus the grab illustrated is suitable for gripping a pile of, concrete slabs or any similar articles which have a fairly fiat horizontal upper surface; other examples are railway sleepers, curb stones, timber, piles of planks and the like.

Each pair of jaw frames 1, 2 consists of two L-shaped side arms 9, 14) or 11, 12. The arms 9 and 11 are firmly connected by ties 13, 14, and the arms 10 and 12 by similar ties 15, 16. The tie 17 not only connects the arms 10 and 12, but also forms the pivot for the arms 9 and 11, so that the jaws 1, 2 can pivot on each other when the grab is raised or lowered.

FIGURE 2 shows the locking device which is omitted from FIGURE 1. An additional tubular tie 18 is shown interconnecting the side arms 9 and 11; this serves as a carrier for the detent 29 described below. To the tubular tie 14 are welded two brackets 20 and 21 which carry a pivotal yoke tube 22. A pair of levers 23 extend from this yoke tube near its ends and carry feeler plates 24 at their free ends. Each feeler plate 24 is preferably made of sheet metal or plastic and is adapted to make direct contact with the upper surfaces of the load. To the yoke tube 22 is secured, at an obtuse angle to the levers 23 (see FIGURES 3 to a fork 25, which is thus rigid with the feeler plate 24. The fork 25 is mounted by a short pillar 26 on the yoke tube 22. The latter also carries, as can be seen in FIGURES 3 to 5, a projecting stop which limits the downward movement of the feeler plate 24.

The additional tubular tie 18 between the arms 9 and 11 carries two brackets 27, 28 supporting a triangular detent 29 mounted on a pivot pin 30 and coupled by a stud 31 to a pawl 32; the later has at its free end a notch or shoulder 33 or equivalent releasable interengagement means which, in the fully open position of the jaws 1, 2, can engage the fork 25. The detent 29 has a tail stop 29a which limits the counter-clockwise movement of the detent, as seen in FIGURES 3 t A small anchor plate 34 is welded radially to the tie 18 and serves as an anchorage for one end of a tension spring 35, whose other end is attached to the pawl 32 at a point 36. To the free end of the pawl is attached another tension spring 38 which is anchored by a bracket 39 to the tie 16 between the arms and 12. On the under side of the tie 16 is attached a trip plate 41 which 'coacts with the detent 29 in the manner described below.

The operation of the locking device is as follows:

Before being lowered onto the load, the jaws 1, 2 of the grab are fully opened (FIGURE 3) and the pawl 32 is engaged with the fork 25., At the same time, the detent 29 locks the trip plate 41 to keep the jaws open before they make contact with the load. When the grab is lowered onto the load, contact is first made by the feeler plate 24 which is forced upwards so that the fork 25 swings to the left (FIGURE 4). This action pulls the pawl 32 to the left against the tension spring 35, and causes the triangular detent 29 to rotate on its pivot pin 30 in a clockwise direction to release the trip plate 41.

When the grab is lifted, the bars 6 move towards the load, grip it and lift it. At this'stage both jaws 1, 2 are firmly held in the operative position. During the lifting, the spring 38 is tensioned and causes the pawl 32 to disengage from the fork 25. The pawl 32 now moves to the position shown in FIGURE 5, and in this final position of the locking device the load is firmly held.

When the grab is lowered and the load placed on the ground, on a truck platform, or the like, the arms 10, 12 of th jaw 2 sink under their own weight and reduce the tension on the spring 38, and the spring 35 pulls the detent 29 counter-clockwise to engage the trip plate 41, so that, after again raising thegrab (with the two jaws 1, 2 now locked in the open position) the feeler 24 can, by gravity, resume its original position asin FIGURE 3, making it ready again to push the pawl to the left and turn the detent 29 clockwise.

Referring now to FIGURES 6 to 8, the grab comprises two L-shaped grab jaws 1, 2 respectively which are connected by a pivot rod 17. Each jaw has a pair of bellcrank side arms, only one of each pair being shown at 9, 10 respectively in FIGURES 7 and 8.

The several pairs of side arms are inter-connected by respective tubular frames, the tubes 13 and 14 for instance connecting the side arm 9 to a corresponding arm (not shown) while the tube 16 connects the side arm 10 to corresponding arm (also not shown). Other such connecting tubes perpendicular to the plane of section in FIGURES 7 and 8 are also provided as necessary.

Between the side arms of the jaw 1preferably in the center of the grab-is a connecting tube 44 extending perpendicularly to the plane of section in FIGURES 7 and 8. The grab bars (not shown) aflixed to the free ends of the grab arms 9 and 10 likewise extend perpendicularly to the plane of section.

A feeler in the form of a two-armed bellcrank lever 23 is provided with a feeler plate 24 which makes contact directly with the load material picked up by the grab, and has a pivoted yoke tube 22 rotatably mounted in brackets 20, 21. A fork 25 fixed to the yoke tube 22 will therefore be deflected in the direction of the arrow 46 when the feeler plate 24 moves in the direction of the arrow 47 after having made contact with the load. The fork 25 engages a notch 33 in a pawl 32 which is thus pulled to the left in the drawings when the fork is deflected to the left. The forward end 32a of the pawl slidably rests on an abutment member 45 afiixed to the tube 13. The purpose of this member will be later explained, The abutment member 45 consists of a slanting plate with an extension 45' upon which the forward end 32a of the pawl 32 actually rests.

The pawl 32 is fastened to a link 48 mounted on a pivot 49. This pivot 49 is at the end of a bar 50 fixed to the tube 16.

Attached to the free end of the link 48 is a tension spring 35. The other end of this spring is fastened to a detent 29, which is pivotally mounted on a pin 30 in a fork-shaped bracket 28 and is associated with another tension spring 51 of which one end, as shown in FIG- URES 7 and 8, is attached to the detent 29 approximately level with tension spring 35, while its other end is anchored on a lug 52 which is fixed to the bracet 28. The lug 52 is non-rotatably fixed to the bracket.

In the position illustrated in FIGURE 7 the detent 29 engages an L-shaped trip plate 41 firmly fixed to the tube 14 of the side arms 9.

The above described locking device functions as follows:

In the position of the two side arms 9 and 10 illustrated in FIGURE 7, these are locked or retained in the open position due to the engagement of the detent 29 with the trip plate 41. As soon as the grab is lowered in this open position upon the load which it is intended to pick up, the feeler plate 24 makes contact with the load and is lifted. This deflects the fork 25 to the left, which in turn pulls the pawl 32 in the same direction, and this displacement of the pawl causes deflection of the link 48 against the resistance of the tension spring 35. As the grab continues to descend, the tension in the spring 35 is progressively increased until the detent 29 disengages the trip plate 41, thus permitting the two grab jaws 1, 2 to close (with the grab bars which are not shown) on the load. The coupling of the feeler 23 to the detent 29 by means of a spring 35 permits the initial contact pressure of the feeler plate 24 on the load to be kept to a minimum. The full pressure required to release the detent 29 from engagement with the trip plate 41 is built up gradually.

When gripping the load, the side arm 9 is pulled further upwards so that the abutment member 45 lifts the pawl 32 out of engagement with the fork 25. The feeler 23, 24 is thus released. The tension spring 51 now deflects the detent 29 counter-clockwise, and permits it to return roughly into the position illustrated in FIGURE 7 except now the trip plate 41 will be above the detent 29. When the grab and the load it has picked up is again lowered, the trip plate 41 moves under the detent 29 which then reengages it, while the notch 33 on the pawl 32 re-engages the feeler fork 25. Hence the two grab jaws 1, 2 are again locked in the open position of the grab.

Other constructions of articulated jaws 1, 2 adapted to grip loads automatically on hoisting can be substituted if desired. Furthermore, the invention is not limited to the specific shapes and configurations of individual components of the jaw locking mechanism as particularly described above, save insofar as said shapes or configurations are essential to the functioning of the parts as required by the appended claims.

I claim:

1. A suspended grab comprising a pair of pivoted jaws; means for raising and lowering the jaws; a detent pivoted on one jaw; a trip member engageable by said detent on the other jaw so as to maintain said jaws in the open position; a pawl linked at one end to said detent. and releasable inter-engagement means at the other end of the pawl,

and a movable feeler releasably engageable at one end with said means on said pawl and adapted at the other end to make contact with a load as the open jaws are lowered thereonto and release said detent from engagement wtih said trip member.

2. A suspended grab comprising a pair of pivoted jaws; means for raising and lowering the jaws; a detent pivoted on one jaw; a trip member engageable by said detent on the other jaw so as to maintain said jaws in the open position; a pawl pivotally connected at one end to said detent and releasable inter-engagement means at the other end of the pawl, and a movable feeler releasably engageable at one end with said means on said pawl and adapted at the other end to make contact with a load as the open jaws are lowered thereonto and release said detent from engagement with said trip member.

3. A suspended grab comprising a pair of pivoted jaws; means for raising and lowering the jaws; a detent pivoted on one jaw; a trip member engageable by said detent on the other jaw so as to maintain said jaws in the open posi tion; a pawl elastically linked at one end to said detent and releasable inter-engagement means at the other end of the pawl, and a movable feeler releasably engageable at one end wtih said means on said pawl and adapted at the other end to make contact with a load as the open jaws are lowered thereonto and release said detent from engagement with said trip member.

4. A suspended grab comprising a pair of pivoted jaws; means for raising and lowering the jaws; a detent pivoted on one jaw; a trip member engageable by said detent on the other jaw so as to maintain said jaws in the open position; a load-contacting feeler pivotally mounted on said one jaw; a pawl releasably engageable by said feeler; a pivotal mounting for said pawl on said one jaw; and a tension spring inter-connecting said pawl and said detent for progressively applying a disengaging force from said feeler to said detent.

5. A grab comprising a pair of pivotally inter-connected load-gripping jaws, each jaw comprising at least one pair of rigidly spaced parallel cranked side arms; a load-contacting feeler pivoted on one of said jaws; a detent also pivoted on the same jaw; a trip member fixed on the other of the jaws and engageable by said detent in the open position of said jaws; a pawl releasably engageable by said feeler, and means for coupling said pawl to said detent whereby deflection of said feeler on contacting a load while the jaws are in the open position causes disengagement of said detent from said trip member.

6. A grab comprising a pair of pivotally interconnected load-gripping jaws, each jaw comprising at least one pair of rigidly spaced parallel cranked side arms; a load-contacting feeler pivoted on one of said jaws; a detent also pivoted on the same jaw; a trip member fixed on the other of the jaws and engageable by said detent in the open position of said jaws; a pawl releasably engageable by said feeler, and an elastic connection between said pawl and said detent for progressively applying a force to said detent to cause it to disengage said trip member as said feeler is deflected by contact with a load.

7. A grab according to claim 6 wherein said detent is resiliently biased to the position of engagement with said trip member.

8. A grab according to claim 7 wherein an abutment is secured to the jaw carrying said trip member for supporting the free end of said pawl in the open position of said jaws.

9. A grab comprising a pair of pivotally interconnected load-gripping jaws, each jaw comprising at least one pair of rigidly spaced parallel cranked side arms; a load-contacting feeler pivoted on one of said jaws; a detent also pivoted on the same jaw; a trip member fixed on the other of the jaws and engageable by said detent in the open position of said jaws; a pawl pivotally connected at one end to said detent and means at the other end for releasable engagement with said feeler whereby deflection of said feeler on contacting a load while the jaws are in the open position causes disengagement of said detent from said trip member.

10. A grab according to claim 9 wherein said pawl is resiliently biased for moving said detent into engagement with said trip member.

11. A grab comprising two pairs of laterally spaced rigidly interconnected cranked side arms constituting loadgripping jaws, each arm having limbs of unequal length and the extremities of the longer limbs of one pair of side arms being pivotally connected at the apex of the angles of the other pair of side arms; a rigid load-gripping member interconnecting the extremities of the shorter arms of each pair; a suspension member connected to the extremities of the longer arms of said other pair of side arms; and releasable locking means for releasably holding said jaws in the open position in which the said longer limbs lie substantially horizontally over a load to be gripped while the shorter limbs depend to embrace the load, said locking means comprising a detent pivotally mounted on one jaw approximately centrally of the longer limbs of the side arms thereof; a trip member fixed on the other jaw for engagement by said detent in the open position of said jaws; a pawl coupled to said detent and lying substantially horizontally when said detent is in engagement with said trip member; a cranked feeler pivoted to the same jaw as the detent and having a longer limb underlying said jaws and inclined downwards to contact the surface of a load in the open position of said jaws while a shorter limb projects upwards to releasably engage said pawl in the open position of said jaws; and spring means connected between the detent and the one jaw for biasing said detent into locking engagement with said trip member.

12. A grab according to claim 11 wherein said pawl is directly pivoted at one end on said detent, and spring means is connected between said pawl and said detent for biasing the latter into engagement wtih said trip member.

13. A grab according to claim 11 comprising a bracket fixed on the jaws carrying said detent; said pawl being pivotally connected to said bracket, and a tension spring coupling said pawl to said detent for applying a trip disengaging force thereto.

14. A suspension grab including a pair of pivoted arms, a locking device adapted for locking the arms in an open position, said device comprising: a feeler constituted by a cranked lever adapted for contacting a load which is to be engaged by the arms of the grab, a pawl supported for pivotal movement on one of the arms, said lever having an end which is engageable with said pawl with the arms in an open position, a detent supported for pivotal movement on said one arm, means connecting said pawl and said detent to pivotally move the latter from a first to a second position as the feeler contacts the load to be engaged by the arms of the grab, and a trip member secured to the other of the arms and engageable by the detent with the latter in said first position to keep said arms locked in the open position and being free of said detent with the feeler in contact with the load which is to be engaged and the detent in the second position thereof.

15. A suspension grab as claimed in claim 14 wherein said trip member is a plate having an end which is engaged beneath the detent with the latter in said first position.

16. A suspension grab as claimed in claim 14, having a first spring with a first end secured on one of said arms and a second end connected to the pawl, a second spring having a first end secured on the other of said arms and a second end connected to said pawl, said pawl being disengaged from the feeler by one of the springs, the detent being urged to the first position thereof by the other of said springs.

17. A suspension grab as claimed in claim 14 wherein said pawl has a notch for accommodating the end of the cranked lever which is engageable therewith.

a spring connecting the detent and the link.

19. A suspension grab as claimed in claim 18 comprising a second spring having one end fixedly secured on the arm with which the detent is supported for pivotal movement, the second spring having another end secured to the detent for urging the same to the first position thereof.

20. A suspension grab as claimed in claim 15 wherein said trip member is of L shape.

21. A suspension grab as claimed in claim 14 comprising an abutment supported on the arm with respect to which the feeler is supported for pivotal movement, said 5 pawl having, a free end supportedon the abutment and being lifted by the abutment as the load is engaged by the grab to be freed from the feeler.

References Cited by the Examiner UNITED STATES PATENTS 10/08 Schuster 294'11O X OTHER REFERENCES German application 1,118,421, Moskopf, printed Nov. 30, 1961, (K1 35b 6/04).

SAMUEL F. COLElVmN, Primary Examiner.

ANDRES H. NIELSEN, Examiner. 

1. A SUSPENDED GRAB COMPRISING A PAIR OF PIVOTED JAWS; MEANS FOR RAISING AND LOWERING THE JAWS; A DETENT PIVOTED ON ONE JAW; A TRIP MEMBER ENGAGEABLE BY SAID DETENT ON THE OTHER JAW SO AS TO MAINTAIN SAID JAWS IN THE OPEN POSITION; A PAWL LINKED AT ONE END TO SAID DETENT AND RELEASABLE INTE-ENGAGEMENT MEANS AT THE OTHER END OF THE PAWL, AND A MOVABLE FEELER RELEASABLY ENGAGEABLE AT ONE END WITH SAID MEANS ON SAID PAWL AND ADAPTED AT THE OTHER END TO MAKE CONTACT WITH A LOAD AS THE OPEN JAWS ARE LOWERED THEREONTO AND RELEASE SAID DETENT FROM ENGAGEMENT SAID TRIP MEMBER. 